Linphone

Linphone is an internet phone or Voice Over IP phone (VoIP). With Linphone you can communicate freely with people over the internet, with voice, video, and text instant messaging.

Free Open Source Mac OS X Windows Linux Android iPhone Android Tablet Web Windows Mobile

MicroSIP

MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack. It allowing to do high quality VoIP calls (P2P or on regular telephones) via open SIP protocol.

Free Open Source Windows

Telephone

Telephone is a VoIP program which allows you to make phone calls over the internet. It can be used to call regular phones via any appropriate SIP provider, including Google Voice via Gizmo5.

Free Open Source Mac OS X

3CX Phone System

3CXPhone is a free VoIP phone available for Windows, iPhone or any Android based smart phone such as Google Nexus, Sony Xperia, Motorola Droid or Samsung Galaxy.

Freemium Windows Android iPhone

YateClient

YateClient is an Instant Messenger and a SoftPhone.

Free Mac OS X Windows Linux

Starfish PBX

Starfish PBX aims to be an open source alternative to Digium’s Switchvox. The goal is to have a software equivalent to which we can add additional functionality like: ...

Free Open Source Linux